Here are just three hopefully relatively budget minded suggestions I have done in the past:
1. I always seem to become good phone friends with the secretaries at the schools, so I ask her to give me a round about time when ALL of my son's teachers are at lunch, and drop off, McDs $1 cheeseburgers, fries and snack wraps. They have always really appreciated this. I also just bake a little extra when I bake and drop stuff to the teachers lounge, they love this, especially during the "off seaons" - in between holidays. I tend to bake alot!
2. A few years ago, I ran into this problem and solved it like this and it was a real hit amongst the teachers. I bought each a mug from the dollar store and enclosed a card, all of the cards had a note in them that talked about how much we really appreciated all they did for us throughout the year, one had a $25 gift card in it that said they had "won" and as much as we appreciated ALL of them this year our budget was tight. They loved it! and appreciated the fact that we were honest about not wanting/being able to spend for each of them. They cards and mugs were put in a basket for them to pick from, so there was no one teacher who had had a better chance than another!
3. This was is my favorite: A few years ago, I took a realitively nice size basket, and filled it with candy each day for a week with an expression 'explaining' the candy, ie If teachers made what they are worth, You would make "100 Grand" - filled with 100 Grand bars, There are not enough "Hugs and Kisses" in the world to say how much we appreciate all you do - filled with Hugs and Kisses, etc. It was placed in the Teachers lounge, annymously, with the help once again of the school secretary. It was me and a friend who did this and it was REALLY cool to hear the teachers talk about what there "secret pals" had left them that day, the final day was a little expensive, we bought fruit and bagels, etc and did a breakfast for them. They secretary who was in on it let us in way early that day and refused to tell who was doing it! She was great! - The expression were all found online or made up by us, cheap, easy and really showed our appreciation to the whole school!
Hope this helps!